Field of the Invention
The invention relates to a drive system for an oscillating pregripper of a sheet-fed printing machine, the pregripper having energy supplied thereto by a controlled drive and in accordance with the position of the pregripper.
Heretofore known drives for pregrippers of sheet-fed printing machines were conventionally formed of a cam gear which was connected to a main drive train of a respective printing machine and drove the pregripper from the drive side of the machine. Because the pregripper is a machine part which has to be accelerated and braked continuously, severe reactions occur on the drive train of the machine. This leads to flank or side changes in the drive and to an excitation of oscillations of the machine and, consequently, to ghosting or slurring, i.e., a degradation of the printing quality. Because of the great forces which occur, a considerable outlay or expense was necessary for the pregripper gearing. The cam gears, in particular, the cam rollers, were subject to great wear. Because this outlay and wear become greater with increasing machine speeds, those concerned with development were forced to seek a solution, in light of the ever faster running machines.
Thus, the published German Patent Document DE 39 22 186 C2 proposed compensating gearing having springs, wherein energy is stored when the pregripper is braked, the energy being removed again for accelerating the pregripper. Because different accelerations of the pregripper are also required, however, at different speeds, various forces occur, depending upon the production speed. In contrast, the proposed attempt at a solution in this German patent document is capable of achieving compensation for only one production speed.
A further proposal was made in the published German Patent Document DE 31 38 540 A1 wherein a pregripper drive is completely separated from the main drive train of the machine and is provided with a dedicated drive, which is controlled by a computer in accordance with the machine position or setting and the machine speed. In this regard, however, the problem arises that, upon the occurrence of any faults in or a failure of the drive electronics, for example as a result of a power failure, a collision of the mechanical systems occurs, which leads to the destruction of the machine.
It is accordingly an object of the invention to provide a drive for an oscillating pregripper of a sheet-fed printing machine, the operational reliability of which is guaranteed.